Catalytic converters for use with internal combustion engines have for many years been made of ceramic honeycomb inserts within a steel housing and inserted in the exhaust line. These converters have a catalytic material carried within the ceramic honeycomb chambers for converting pollutant materials such as carbon monoxide, ozone, nitrogen oxides, unburned hydrocarbons, etc., to harmless gases, e.g., carbon dioxide, nitrogen, water, etc. Ceramic converter elements have a number of problems including cost, manufacture at a point remote from the point of assembly, and fragility.
Recently, developments have been made in such catalystic converters whereby the ceramic element has been replaced with a corrugated thin metal, accordion folded element having a baked on or in situ formed coating of aluminum oxide onto which catalystic materials, such as platinum, palladium, rhodium, etc., may be deposited. These devices may be manufactured at a single site, lack fragility and are relatively inexpensive. Reference may be had to my copending application Ser. No. 830,698 filed Feb. 18, 1986, which discloses a process for making such nonnesting corrugated thin metal element containing catalystic converters.
In the fabrication of these devices, while various cross-sectional configurations can be made, a convenient configuration is one which is circular. Such circular devices are generally formed from a herringbone corrugated thin metal strip which is folded in a zig-zag manner, or accordion folded back and forth upon itself, with each fold gradually increasing in length up to the diameter desired, and then gradually decreasing in length to the shortest chord acceptable in the steel housing. The herringbone or chevron pattern of the corrugations prevents nesting of the overfolded folds and maximizes the open area through the core element.
These structures, when inserted in an internal combustion engine exhaust line are submitted to cyclic vibrations due to the normal pulsing of the engine, and to a large axial force as well as high temperatures. Automotive manufacturers, for example, have adopted what is known as a "Shake and Bake Test" in accordance with which the device is submitted to an axial force of 60 g's, a temperature of 1560.degree. F., and vibrated at a frequency of 155 Hertz with engine exhaust flowing. Normally, these devices will fail in a few hours, e.g., 26 hours. The standard which must be met is at least 100 hours for certain applications. On occasion 10 hours is satisfactory. Failure in corrugated metal core devices is evidenced by a shifting of the corrugated folds in such a manner that they nest, and thus effect a change in diameter. Under the axial forces applied, portions of the element actually move in an axial direction with respect to the housing, and the device fails.
It has now been found that by inserting "struts" at one or more intervals between folds and extending axially for the length of the element, such struts being otherwise disconnected from the overfolded or layered portions, the devices will meet the standards determined for the "Shake and Bake Test".